Chemical mechanical polishing (CMP) is a technique which has been conventionally used for the planarization of semiconductor wafers. For example, see U.S. Pat. No. 5,099,614, issued in March in 1992 to Riarai et al; U.S. Pat. No. 5,329,732 issued July 1994 to Karlsrud et al, and U.S. Pat. No. 5,498,199 issued March 1966 to Karlsrud et al. Furthermore, chemical mechanical polishing is often used in the formation of microelectronic devices to provide a substantially smooth, planar surface suitable for subsequent fabrication processes such as a photoresist coating and pattern definition. A typical chemical mechanical polishing apparatus suitable for planarizing a semiconductor surface generally includes a wafer carrier configured to support, guide, and apply pressure to a wafer during the polishing process, a polishing compound such as a slurry to assist in removal of material from the surface of the wafer, and a polishing surface such as a polishing pad.
A wafer surface is generally polished by moving the surface of the wafer to be polished relative to the polishing surface in the presence of a polishing compound. In particular, the wafer is placed in a carrier such that the surface to be polished is placed in contact with the polishing surface, and the polishing surface and the wafer are moved relative to each other while slurry is supplied to the polishing surface.
Semiconductor wafers used in the manufacture of integrated circuit are subjected to a plurality of fabrication steps. These steps may involve the growth or deposition of insulating layers, the deposition of metal or other conductive layers, impurity doping, photolithographic patterning and the like. These steps are often preceded or followed by cleaning steps which involve, for example, scrubbing, spray cleaning, musing and the like. At the completion of the cleaning step, the wafer is further processed to remove water or cleaning agents so as to prevent the water and/or cleaning agent from drying and leaving a contaminating residue on the wafer surface. In the current state of the art, the last step in a cleaning procedure usually comprises a rinsing step utilizing ultra-pure (deionized) water followed by a drying step.
Spin drying is a process commonly used to remove liquid residue from the surface of a wafer. In such a process, the wafer is spun about its axis at a high rotational velocity such that centrifugal force drives the liquid radially outward and off the edge of the wafer. Spin drying is accomplished by placing the wafer in a spin rinse drier (SRD) comprising a platform that is coupled to a drive motor. The drive motor causes the platform to spin at a velocity of, for example, 1000-4000 rpm. In the past, such wafers were comprised, in part, of a metal (e.g. copper) and a hydrophilic oxide (e.g. TEOS as the inner layer dielectric (ILD) oxide). Water wets a hydrophilic surface; i.e. a thin layer of water spreads relatively evenly over the wafer surface and flows off the edge of the wafer upon the application of centrifugal force as described above. As the wafer dries, only a small amount of residue is left on the wafer surface. Due to the need for faster integrated circuitry, however, there has been increased use of low dielectric constant (K) dielectrics such as carbon doped oxides and spin-on materials (e.g. polyimide) which exhibit hydrophobic characteristics; i.e. they repel water. Water beads on hydrophobic surfaces, and as the hydrophobic nature of a material increases, the contact angle of a bead of water on the surface increases. This beading phenomenon results in greater amounts of water residing on smaller defined areas of the wafer surface. While drying (i.e. spinning in an SRD), the resulting centrifugal force on each bead of water causes each bead to roll toward the edge of the wafer. Unfortunately, as the bead rolls toward the edge of the wafer, it leaves droplets of water behind that dry leaving contaminants on the surface. These contaminants appear as radial lines or streaks corresponding to the trail of droplets left by the bead as it rolled toward the wafer's edge. The amount of contaminant left on the hydrophobic surface exceeds that left on a hydrophilic surface because of the beading and because the failure to “wet” the surface results in inferior cleaning. The resulting local areas of contaminants may significantly reduce yield, overload metrology systems, and create problems in devices produced on the wafer.
In view of the foregoing, it should be appreciated that it would be desirable to provide an improved apparatus and method for rinsing and drying a hydrophobic surface such as a hydrophobic surface of a semiconductor wafer.